Levulinic acid is a major product of the controlled degradation of sugars by acid hydrolysis. Although levulinic acid has been known since the 1870's, it has never attained much commercial significance. One of the reasons for its slow development is the cost of the raw materials for synthesis. Another reason is the low yields of levulinic acid obtained from most synthetic methods. These low yields are largely due to the inherent physical properties of levulinic acid which do not allow for its facile recovery. Moreover, the production of levulinic acid has had high associated equipment costs. Given these factors, therefore, the production of levulinic acid has not appeared to be commercially feasible.
Despite the inherent problems in the production of levulinic acid, however, the reactive nature of levulinic acid makes it an ideal intermediate leading to the production of numerous useful derivatives. Levulinic acid, therefore, is desirable as a basic chemical raw material. See R. H. Leonard, "Levulinic Acid as a Basic Chemical Raw Material," Industrial and Engineering Chemistry, Vol. 48, p.1331-41 (1956).
The formation of levulinic acid from low-cost cellulosic material could, however, overcome one of the major difficulties encountered in other synthetic processes. By starting with waste biomass the cost of the starting material for production of levulinic can be greatly reduced. Moreover, the supply of sugars from cellulose-containing plant biomass is immense and replenishable. Most plants contain cellulose in their cell wall. For example, cotton is 90% cellulose.
Furthermore, it has been estimated that roughly 75% of the approximate 24 million tons of biomass generated on cultivated lands and grasslands is waste. This cellulose that is derived from plant biomass could be a suitable source of sugars to be used in the process of obtaining levulinic acid. Thus, the conversion of such waste material into a useful chemical, such as levulinic acid, would be desirable.
Sugars are converted to levulinic acid essentially by a process of dehydration and cleavage of a mole of formic acid. See Reid H. Leonard, supra. The literature in the art suggest that levulinic acid can be formed quite readily from glucose and other sugars by the action of boiling the sugars in a dilute acid solution. See P. T. Sah and S. Y. Ma, "Levulinic Acid And Its Esters," J. Amer. Chem. Soc., 52:4880 (1930); and L. Fieser and M. Fieser, "Reagents for Organic Synthesis," John Wiley and Sons, Inc. 1967, p. 564-66.
In the literature concerning production of levulinic acid from sugars, however, generally HCl is used as the acid source in the dehydration reaction of sugars. See L. Fieser and M. Fieser, supra.; Alva Thompson, U.S. Pat. No. 2,206,311; Wendell W. Moyer, U.S. Pat. No. 2,270,328; Georg Scheuing and Wilhelm Konz, U.S. Pat. No. 2,305,738; Walter N. Haworth and Leslie F. Wiggins, British Patent No. 583,533. Sulfuric acid has been used as the acid source in dehydration reaction of bran, the here the reported product is furfural, rather than levulinic acid. See Paul Karrer, "Organic Chemistry," 2nd ed, Elsevier Publishing Co, Inc., New York 1946, p.737.
The theoretical yield of levulinic acid from a hexose is 64.5%. The literature in the art, however, indicates that only about two-thirds the theoretical yield can be attained in the presence of dilute HCL. Interestingly, substantially the same yields were obtained from cellulose in Douglas fir sawdust. See Reid H. Leonard, supra. Thus, it appears possible to utilize cellulosic materials to produce sufficient quantities of levulinic acid to be used as a basic raw chemical material.
If a low-cost production of levulinic acid could be achieved, such as the formation of levulinic acid from low-cost cellulosic material, the useful derivatives of this chemical are numerous. For example, esters of levulinic acid are used for flavoring, and some have been reported to be used as plasticizer. Reaction of levulinic acid with carbonyl reagents also can yield numerous derivatives, many of which are hydrazones and semicarbazones. These derivatives are of interest for conversion into pyridaziones and for the preparation of soluble derivatives of insoluble, but biologically active, materials. Also alkyl metal halides react with levulinate esters to yield a series of .gamma.-substituted .gamma.-valerolactones, some of which may be used for perfumes and flavors.
Oxidation products of levulinic acid are also known. These include the peroxide, methyl vinyl ketone, and succinic, malonic, and acetoacrylic acids. These derivatives have been postulated to be of use in foods, and as solvents in liquid-liquid extractions of hydrocarbons. In addition, the 4-amino derivatives of levulinic acid readily forms lactams and 5-methylpyrrolidones, while the amides upon hydrogenation of the keto group, also form 5-methylpyrrolidones.
Upon distillation, dehydration of levulinic acid occurs and .alpha.-angelica lactone (.gamma.-lactone of 4-hydroxy-3-pentenoic acid) is formed together with some .beta.-angelicalactone (.gamma. lactone of 4-hydroxy-2-pentenoic acid). Various heterocyclic compound are also derived from levulinic acid. Some of these are pyrones, dioxanes, a coumarin, and thiazocines, which have been proposed for use as bacteriostatic and analgesic agents.
Moreover, substitution of levulinic acid for a portion of the acetyl groups in vinyl acetate-containing resins and cellulose acetate has been shown to yield materials of increased strength. The .alpha.-angelica lactones, one of the simplest products to be made from levulinic acid, can also be converted to a series of pseudolevulinic acid derivatives and has also been reported to be a means of obtaining 3-chloro-levulinic acid.
Reduction products of levulinic acid are also important. It has been reported that catalytic hydrogenation at temperatures above 200.degree. C. yields substantial amounts of 1,4-pentanediol, and smaller amounts of .alpha.-methyltetrahydrofuran, and 1-pentanol. See Reid H. Leonard; G. Natta, R. Rigamonti and E. Beati, "The Hydrogenation of 2-furaldehyde And Its Derivatives," Chimica e Industria (Italy) 23, 117-23 (1941).
In all, the exceptional reactivity of levulinic acid and its lactones coupled with its availability from waste biomass provide an ideal set of conditions for the use of levulinic acid as a basic chemical raw material. Thus, there exists a need to be able to produce levulinic acid. Moreover, it would be most desirable to be able to produce levulinic acid in an economically viable and environmentally safe process.